Apparatus for the recovery of sulphuric acid



H. W. SHELDCN APPARATUS FOB THE RECOVERY 0F SULPHURIC ACID Fe@ 22, E933 Original Filed Nov. l0, 1934 Z'Sheets-Sheet l INVENTOR TORNEY Feb. 22, 1938. W SHELDON 2,108,870

APPARATUS FOR THE RECOVERY 0F SULPHURIC ACID 2 Sheets-Sheet 2 INVENTOR 7.4 m@ TORNEY` Patented Feb. 22, 1938 UNITE STATES ATENT OFFECE APPARATUS FOR THE RECOVERY OF SULPHURIC ACID Original application November 10, 1934, Serial Divided and this application July 2, 1936, Serial No. 88,569

3 Claims.

This invention is directed to apparatus for the recovery, concentration, and purication of sulphuric acid which has been used in the treating oi hydrocarbon oils. It is specifically directed to the application of this apparatus to obtain recovered acid oi high purity and concentration from spent acids used in the treatment of lubrieating oils.

It has been proposed heretofore to heat recovered acid in a quiescent body out oi Contact with products of combustion in order that organic carbonaceous impurities contained ther-ein might be oxidized. Such processes as have been proposed operate at a temperature level in the neighborhood or" the boiling point of 89-9i% sulphuric acid. The product or recovered acid obtained by treatment at these temperatures is usually not suiilciently high in purity for many oil refining uses. It is usually black and contains considerable quantities of dispersed carbonaceous m tcrials. The uantity or this material may vary over wide limits depending upon the source of the recovered acid and the care used in operating the concentrating equipment. It is not uncommon to nd acid reclaimed from the treatment of lubricating oils which contains in excess of 1% of combustible organic material. This black acid is particularly troublesome in the treatment of oils requiring high finished color, as it may impart color to them. It is also quite troublesome where a continuous acid treating process employing centrifuges for separation of oil and acid sludge is used, since the carbonaceous material deposits upon the centrifuge bowls and rrequires frequent shut downs for cleaning. Prior art processes o which I am aware are also subject to considerable trouble and loss of acid by fuming when operating at high temperature levels such as are necessary for even partial removal of the carbonaceous material. Of course a portion of these fumes maybe recovered by the use of suitable precipitation equipment, such as the Cottrell apparatus, but the operation of this equipment introduces another operative step and further eX- pense. Since the temperatures of operation of prior art processes are limited by fuming and similar difficulties, the time element for complete cleanup of acid is necessarily long, requiring extensive equipment installation. Similarly, the fume loss limitation on temperature levels restricts the previously proposed processes to the production of acid of about 90% strength, since sufficient temperature is not available for the concentration or acid to higher strength.

It is therefore an object of this invention to (Cl. .2S-276) devise an apparatus wherein a proper method for the purication of sulphuric acid may be conducted under conditions and at temperature levels capable of substantially removing carbonaceous materials found troublesome when the acid is used in oil rening. Further objects are the attainment of compactness and efficiency in the apparatus for this process, and such'other objects and advantages as may be pointed out hereinafter.

All of these objects and advantages are obtained by my improved process, and are obtained to a particular degree when that process is carried out in my preferred form of apparatus.

In order that my process and apparatus may be clearly understood, reference is now made to the drawings which are attached to and made a part of this specification. In these drawings, Figure l is a sectional elevation of a preferred form oi apparatus and Figure 2 is a plan view of the same, Figure 3 is a section of a particular form of burner for use inthe apparatus, Figure e is a vertical view, partially in section, of another form of burner construction, Figure 5 is a horizontal section through the burner shown in Figure d,

and Figure 6 is a horizontal section through still another type of burner.

In Figure l, 'l represents a preheating tower, packed with ceramic contact material 8, over which acid to be treated is fed through line 9, falling upon distributor I. The ceramic packing material is retained in the tower by a proper grid Ii, and the acid from the tower discharges through the throat I2 into the concentration pot I3. This concentration pot is equipped with an overflow line Ill or the removal of treated acid, and a grating I5 prevents the passage of scum and coagulated impurities into the overow line. This overflow line I4 leads to acid cool-ers` which are not shown. Heat is applied to the concentration pot by a series of burners I, which are later explained in detail. The gases of combustion from these burners It are collected in manifold Il' and passed into the preheating tower by flue I8. Further air for use in the preheating tower is! introduced from the atmosphere by means of fan It, conduit and manifold 2l. The use of nue gases from. burners I6 in the preheating tower is optional, and the tower may be heated, if desirable, by heat from other sources, such as waste heat from the ordinary concentration pans, or it may even be heated by a separately fired furnace. Y

The burner used is shown in Figure 3, and is an internally iired vsurface combustion burner.

As seen in Figure 3, it is composed of a tube 22, adapted to be mounted in the roof of the concentration pot and to depend thereinto, with its lower end submerged in the acid undergoing treatment. This mounting is facilitated by .a moulding 23 surrounding the upper end of the tube which may rest in a corresponding seat in the roof of the concentration pot. Mounted upon the tube 22 at its top end is a cross 24 of suitable material, such as transite which is a mixture of asbestos and certain mineral cements, cr of ceramic material. It is possible, so far as corrosion from flue gas is concerned, to make this fitting and all other flue gas parts of metal, but because they are exposed externally to a corrosive atmosphere, I prefer some such material as the transite mentioned. 'Through the upper end of the cross 24, I insert burner 25, and support it therein by plate 26, which also serves to close this opening of the fitting 24. Burner 25 consists of two concentric tubes 21 and 28. The outer tube 21 is connected to a suitable source of air under a suflicient pressure, and the inner tube 28 is connected to a source of supply of combustible gas. bustion mixture I have inserted in tube 21 a pair of properly insulated wires, designated 29, leading to a spark gap at the termination of the concentric tubes. The space within the tube 22 outside of tube 21 is packed with a granular or ring formed ceramic packing. When the gas stream is ignited, surface combustion occurs in this packing, and the extremely high temperatures therein generated are readily transferred to the acid through the walls of tube'22. Tube 22 is preferably made of a high silicon cast iron, fused quartz, or other material resistant to both acid and temperature.

To provide rapid transfer of heat, I may increase the surface of muille 22 by corrugations or ns. For instance, I may adopt the construction shown in Figure 4, wherein the external surface of the tube 22 is provided with longitudinal fins 33, more clearly seen in Figure 5, which is a horizontal section ofthe tube shown in Figure 4. If desired, the surface of tube 22 may be ribbed both inside and outside, as shown in Figure 6.

Instead of the surface combustion used in Figure 3, I may employ an open type of combustion, in which case I construct the tube 22 with an internal concentric mufile as indicated by numeral 34 in Figures 4, 5, and 6. In this case, the burner tubes 21 and 28 are positioned within the mufe 34, near its upper end. In some cases I find that it is preferable to use the muifle 34 even when using a surface combustion operation, and in this case, the interior of the muille tube 34 below the end of the burner tubes will be packed with granular or ring-formed ceramic material. In any case, the use of the internal annular muiile is conducive to high rates of heat transfer, since the hot gases will pass out of the lower end of the muifle and up along the inner walls of the tube 22 at a high velocity conducive to a high rate of heat transfer.

To return to Figure 3, I dispose of the gases of combustion through a tube 32, tted into one side outlet of the cross 24. In case these gases are not used in the preheating tower, this tube 32 leads to a stack and the other side outlet of cross 24 is suitably plugged. If, as preferred, these gases of combustion are used in the preheating tower, they are at too high a temperature for that use as they come from burner tube 22. To lower their temperature, I introduce air In order to ignite the comfrom the atmosphere through tube 3| inserted in the other side outlet of cross 24. In this preferred setup, referring to Figure l, tube 32 connects the burner to manifold l1 and tube 3l connects it to manifold 2|. These tubes 3l and 32 are both equipped with butterfly valves in order that properly balanced conditions of air and gas ow may be maintained.

The method of operation is as follows: Untreated black recovered acid, preferably concentrated already to a strength of iQ-91% such as may be had by exposure to temperature Yof the nature of 540 F. is introduced to the top of preheating tower 1, and trickles down over the packing material therein. In that tower it encounters hot gases, and is preheated thereby to a temperature of approximately 425 F. In order to avoid the formation of fumes of S03 and the loss of acid thereby, the temperature of the preheating gases is adjusted so that they are not above approximately 700o F. at the time of rst contact with the acid. I obtain control of this gas temperature preferably by diluting combustion gases with air, as pointed out above. I also find that the level of temperature of the acid at the throat (l2) of the preheating tower is of impartance in the avoidance of fumes, although the control at this point is not particularly delicate, and the temperature may vary from 400 to 600 F. The preferred temperature, however, is 428 F. to 430 F. The acid leaving the tower drops into the body of acid in the concentration pot, which is maintained at a temperature of 620- 630 F. Indirect heating at this temperature level not only serves to destroy the black carbonaceous organic impurities in a very short time, but also concentrates the acid to a strength in the neighborhood of 98%. I regard this temperature level of the concentrating pot as an important element of my process. It is high enough to bring about eifective elimination of the carbonaceous impurities. It is likewise high enough to accomplish that elimination in a comparatively short time and enable a high throughput rate in the apparatus. l It is also sufficiently elevated to effect the concentration of the feed acid to a strength of approximately 98%. Coupled with the controlled temperature level, I am enabled to bring about these desirable results without fume trouble or loss of sulphuric acids as fumes, and consequently do not have to resort to expensive precipitation devices. I encounter is that of an amount of SO2 proportional to the amount of carbonaceous material in the black acid and produced during the elimination thereof. No one of the prior processes of which I am. aware is capable of producing concurrently these results of high cleanliness, high concentration, and low loss. To accomplish these results, I iind that the temperature level must be maintained near the range specified, and that when they are so maintained, a reaction time of approximately one hour is required in the concentration pot.

I have herein disclosed a new process clothed in a distinctive type of apparatus, which apparatus is highly adapted to this process. Certain equivalent constructions have been disclosed, and other equivalents may be suggested to those skilled in the art. All of these variations I deem to bea part of my invention, and claim them as such, subject to the limitations to be found in the following claims.

This case is a division of my co-pending ap- The only loss plication Serial No. 752,397, filed November 10, 1934.

I claim:

l. In apparatus for the regeneration of sludge acid, a contact tower through which acid may pass in countercurrent to and in contact with heated gases, feed means to introduce acid to said contact tower, means to introduce heated gases to said tower at a point between its ends, thereby dividing said tower into a preheating zone above said gas inlet and a fume absorption Zone below said inlet, means to control the temperature of said heating gases, an acid concentrating zone adapted to contain a body of acid, communication means between said absorption zone and said concentrating zone, sealing means to cover said concentrating zone to prevent access of air thereto and to compel gases therefrom to pass through said preheating Zone, discharge means to remove concentrated acid from said concentrating zone heating means for said concentrating zone, comprising an elongated closedended vessel of impervious heat-conductive material depending into said concentrating zone and extending to a point substantially below the surface of the acid in said zone, means tomaintain a combustion within said vessel, and means to remove the products of combustion therefrom while preventing their contact with the contents of said concentrating zone.

2. In apparatus for the regeneration of sludge acid, a contact tower through which acid may pass in countercurrent to and in contact with heated gases, feed means to introduce acid to said contact tower, means to introduce heated gases to said tower at a point between its ends, thereby dividing said tower into a preheating zone above said gas inlet and a fume absorption zone below said inlet, an acid concentrating zone adapted to contain a body of acid, communication means between said absorption zone and said concentrating zone, sealing means to cover said concentrating Zone to prevent access of air thereto and to compel gases therefrom to pass through said preheating zone, discharge means to remove concentrated acid from said concentrating zone, heating means for said concentrating zone comprising an elongated closed-ended vessel of impervious heat-conductive material depending into said concentrating Zone and extending to a point substantially below the surface of the acid in said zone, means to maintain a combustion within said vessel, means to remove the products of combustion therefrom while preventing their contact with the contents of said concentrating zone, means to admix air with said combustion gases to lower their temperature, and means to convey the mixed gases to the heated gas inlet of the preheating zone.

3. In apparatus for the regeneration of sludge acid, a preheating zone through which acid may pass in countercurrent to and in contact with heated gases, below said preheating zone an absorption zone into which the acid passes from the preheating zone and below said absorption zone a third zone containing a quiescent body of acid, feed means to introduce acid to said preheating zone, communication means between said absorption Zone and said third zone, withdrawal means to remove acid from said third zone, heating means for said third zone comprising an impervious heat conductive vessel depending thereinto to a point below the surface oi the acid in said zone, means to maintain a combustion within said vessel, means to prevent exposure of the acid in said third zone to oxidizing gases and to cause gases generated therefrom to pass into said absorption zone, means to introduce heating gases into said preheating zone, and means to control the temperature of said heating gases.

HOWARD W. SHELDON. 

